The invention relates to a method of purifying waste water biologically, and to bacteria and a mixed bacterial population suitable for the method and the use thereof. The invention further relates to a bioreactor comprising said bacteria or mixed population.
Conventionally, water can be purified both by physical and chemical means, for example by sedimentation, filtration or flocculation (WO94/5866 and WO88/5334). In order to remove organic compounds and other compounds that are difficult to purify it is also preferable to use so-called biological purification wherein the water to be purified is brought into contact with microorganisms that decompose pollution agents. Biological water treatment methods are suited for use both in conventional water treatment plants and industrial waste water treatment plants. Biological water treatment has also been tested in systems where water is recycled (Fl 964141). Biological water treatment is also needed to purify seep water of a dump, for example, before the seep water is discharged into the environment.
The biological purifying method is, however, more difficult to control than the physical or chemical purifying methods. Firstly, microorganisms to decompose pollution agents must be found. Secondly, the microorganisms must be capable of easily surviving and reproducing under conditions during the water treatment process. In other words, the microorganisms used for purifying water must be competitive ones so as to prevent other organisms in the water from overruling. In addition, the microorganisms used for purifying water must not be sensitive to the changes in their environment that often occur during water treatment processes when the load varies.
Many kinds of microorganisms have been used for purifying water, including bacteria and protozoa, such as the ciliates. Bacteria that have often been used include species of the Pseudomonas genus, but also members of the Alcagenes, Acinetobacter or Rhodococcus genera are often used. Mixed populations, some identified and some unidentified, comprising a great number of different microorganisms are often used. Aerobic or facultative microorganisms are best suited to purifying water, in which case it is appropriate to pump air into the water to be purified so as to make the purification process more efficient.
When microorganisms are cultivated, the growth medium should normally be sterilized so as to prevent the cultivation from becoming contaminated by external organisms. Since large amounts of water are processed while purifying waste water, the amount of necessary biomass for the biological purification is also large. To produce such biomass under sterile conditions is both laborious and expensive; hence, it would be most desirable if the biomass could be produced under non-sterile conditions without any danger of becoming contaminated. The present invention now provides a novel fermentation technology with no need to sterilize. This is possible when microorganisms particularly suitable for the method are used and these microorganisms are fed on nutrients suitable for them.
The present invention relates to microorganisms that are surprisingly well suited to biological purification of waste water. These microorganisms meet particularly well the aforementioned requirements set for microorganisms suitable for the biological purification of water. In addition, the microorganisms of the invention are so specific that their biomass can be produced under non-sterile conditions by using a growth medium where other microorganisms are unable to compete. This enables large savings in the costs and energy consumption of a biological water purification process, the purification results also being excellent. Water purified according to the invention is even recyclable.
The invention thus relates to the bacteria Bacillus sp. DT-1 having the deposit number DSM 12560 and progeny thereof, Pseudomonas sp. DT-2, subsequently identified as Pseudomonas azelaica having the deposit number DSM 12561 and progeny thereof, and the former Pseudomonas sp. now being Rhizobium sp. and having the deposit number DSM 12562 and progeny thereof. Later 16S rDNA analyses have shown that this bacterium most closely resembles the members of the Rhizobium genus, so hereafter, it will be considered as one of them. The invention further relates to the following bacterial strains promoting water purification: Pseudomonas azelaica DT-6 having the deposit number DSM 13516, Azospirillium sp. DT-10 having the deposit number DSM 13517, Ancylobacter aquaticus DT-12 having the deposit number DSM 13518, and Xanthobacter sp. DT-13 having the deposit number DSM 13519, and progeny thereof. DSM 12560-12562 have been deposited at Deutsche Sammlung von Mikroorganismen und Zelikulturen GmbH on 1 Dec. 1998, and DSM 13516-13519 on 29 May 2000.
The invention further relates to a bacterial mixed population characterized by comprising the bacterium Bacillus sp. DT-1 having the deposit number DSM 12560, Pseudomonas azelaica DT-2 having the deposit number DSM 12561, and/or Rhizobium sp. DT-5 having the deposit number DSM 12562, and progeny thereof.
The invention further relates to the use of the aforementioned bacteria or bacterial mixed populations in waste water treatment and to a method of purifying waste water, characterized by purifying water biologically by microorganisms belonging to the group Bacillus sp. DT-1 having the deposit number DSM 12560, Pseudomonas azelaica DT-2 having the deposit number DSM 12561, and Rhizobium sp. DT-5 having the deposit number DSM 12562, and progeny thereof.
The invention further relates to a bioreactor characterized by comprising microorganisms belonging to the group Bacillus sp. DT-1 having the deposit number DSM 12560, Pseudomonas azelaica DT-2 having the deposit number DSM 12561, and Rhizobium sp. DT-5 having the deposit number DSM 12562, and progeny thereof. A bioreactor is a reactor in which a biological purification process is conducted.